Method for manufacturing heat-sealable packaging material having barrier layer; containing cycloolefin copolymer

ABSTRACT

Method of manufacturing polymer-coated heat-sealable packaging material and sealed packages (e.g., carton, box, or bag packages for dry and liquid foods). The material includes a fiber base of packaging paper or packaging board, an outer polymeric heat sealing layer such as LDPE, and an inner polymeric water vapor barrier layer which is partly or totally formed of an amorphous cycloolefin copolymer. In the method, the cycloolefin copolymer water vapor barrier and the heat sealing layers are brought onto the fiber base by an extrusion step, and in accordance with the manufacturing method, they can be placed on one side of the fiber base or on both sides of the fiber base for achieving a moisture barrier on both sides of the package. Also, polymeric oxygen barrier layers, such as EVOH or polyamide layers, can be incorporated into the packaging material. By using the cycloolefin copolymer as an extruded water vapor barrier layer, curling of the packaging material is prevented.

The invention relates to a method for manufacturing a heat-sealablepackaging material, in which superimposed polymeric coating layers areextruded onto a fibre base, the layers comprising an outer polymericheat sealing layer and at least one inner polymeric barrier layer, thewater vapour permeability of which is lower than that of the heatsealing layer. Further, the invention relates to a polymer-coatedpackaging material provided by the method and to a finished, sealedpackage manufactured of it by folding and heat sealing.

Tightness is required from the product packages for liquid and even manydry foods both for preventing the premature deterioration of the productand also to protect the packaging material itself. The water vapourtightness of the material prevents the liquid product from leaking fromthe package and the fibre base of the material from becomingwater-soaked due to the moisture absorbing from the product. The watervapour tightness also prevents the access of external moisture to damagethe packed dry product. In addition, it is often required that thepackaging material be oxygen tight to-prevent the oxidation of thepacked product and to preserve its aromas.

The low-density polyethylene (LDPE) generally used in the uppermost heatsealing layer of fibre-based polymer-coated packaging materials alsogives protection against the permeation of water vapour. However, LPDEis not a very efficient material in this respect, and for achieving agood water vapour barrier it has to be used as a relatively thick layer.High-density polyethylene (HDPE) is used in fibre-based packagingmaterials as a considerably more efficient polymer forming the watervapour barrier, the layer containing HDPE being typically placed insidethe packaging between the heat sealing layer and the fibre base and thepossible oxygen barrier layer so that, besides the fibre base, the watervapour barrier also protects the oxygen barrier from moistening causedby the packed product.

However, the drawback of the use of HDPE in fibre-based packagingmaterials has been the curling of the material caused by it. The reasonfor this is the postcrystallization taking place in the HDPE layer afterits extrusion.

The object of the invention is to form a solution, with which the saidcurling problem of the fibre-based packaging material can be avoidedwithout it being necessary to compromise over the water vapour barrierarranged to the material. It is characteristic of the manufacturingmethod of the packaging material of the teristic of the manufacturingmethod of the packaging material of the invention that cycloolefincopolymer (COC) is incorporated in the barrier layer so that theextrusion produces an amorphous layer without the post-crystallizationoccurring in the polymer.

Cycloolefin copolymers (COC) are polymers that are produced bycopolymerising ethene and cycloolefin and that are disclosed, forexample, in the publication print EP 0 773 102 A1, which with referenceis incorporated as part of the present explanation. It is characteristicof COC that it has good water vapour barrier properties; in addition, itis amorphous. Thus, neither post-crystallization nor curling caused bythis occur in the extruded COC layer. As water vapour barrier it solvesthe above-mentioned problems related with HDPE used according to thestate of the art.

The examples in the publication EP 0 773 102 A1 specifically describecycloolefin copolymers, which are tetracyclic. In addition, commercialCOC polymers manufactured by copolymerising ethene and norbornene areavailable, which have a high density and water vapour barrier propertiesat least similar to those of HDPE. The company Ticona GmbH manufacturingsuch COC reports its products to have the density of 1.02 g/m³, theelasticity modulus of 2600-3500 N/mm², and the water permeability of0.02-0.04 g·mm/m²·24 hours. COC has been marketed as water vapour tightmaterial for polymeric blister packages and packaging films, but as faras is known to the applicant, COC has not been used for fibre-basedpackaging materials, such as packaging paper and board, as water vapourbarrier to be extruded according to the invention, the purpose of whichis to avoid the curling problems of the previous materials.

The barrier layer containing COC can be attached in extrusion directlyto the heat sealing layer of LDPE without it being necessary to apply abinding agent between the layers. COC as such is not heat-sealable, butit can be heat-sealed combined with LDPE. Further it has been noted inaccordance with the invention that the COC barrier layer can inextrusion be attached to the fibre base likewise without the bindingagent layer between them. Thus, the invention makes possible a packagingmaterial embodiment, in which the one side of the fibre base is onlyprovided with superimposed COC and heat sealing layers at the same timeas the opposite side of the fibre base can be left totally without thepolymer coating. The manufacture of a respective material by using HDPEas the water vapour barrier would not at all be possible, because of thecurling problem. The material is useful for packages for dry products,in which the polymer layers come to the external surface of thepackaging to protect the fibre base and the packed product from externalmoisture.

Alternatively, the invention can be advantageously applied by extrudingthe super-imposed COC and heat sealing layers to both sides of the fibrebase of the packaging material. It is possible that the material has asymmetrical structure, in which case it can be applied to the foldedpackage either way, without changing the other properties of the watervapour barrier or the package.

According to the invention, the water vapour layer can consist merely ofCOC or, alternatively, of a mixture of COC and some other polymer, suchas LDPE. COC in itself is a relatively rigid polymer material, and byblending it with LDPE, it is possible to reduce the risk of rupturesimpairing the vapour barrier when the packaging material is folded topackages.

According to the invention, the weight of the COC layer forming thewater vapour barrier can be 5-50 g/m², preferably 7-30 g/m², and mostpreferably 10-20 g/m². The weight of the heat sealing layer, which ispreferably made of LDPE, can be 5-50 g/m², preferably 5-30 g/m², andmost preferably 7-20 g/m². By blending some other suitable polymer, suchas polypropylene or polybutene, with LDPE in the heat sealing layer, itis possible to achieve a peeling joint sealing, i.e. a joint sealing,which opens when pulled apart.

At least one polymer layer forming an oxygen barrier can further beincorporated in the packaging material of the invention. When, forexample, liquid foods are packed, the packaging material is typicallyfolded so that the oxygen barrier comes to the interior of the fibrebase. COC water vapour barrier layers can further be advantageouslyarranged to both sides of the material so that the fibre base and theoxygen barrier are left between two COC layers. The polymer layersinside the package then form the oxygen and water vapour barrier, whichprotects the packed product from the open air, and simultaneously, thefibre base of the packaging material from the packed product. The COCvapour barrier layer outside the package again protects the fibre baseand the oxygen barrier from moisture penetrating from the outside andensures that the package will keep its barrier properties during thepreservation period required from it.

Suitable polymer materials forming the oxygen barrier are ethylene vinylalcohol copolymer (EVOH), polyamide (PA), and the compounds of these.The weight of the oxygen barrier layer to be incorporated in thematerial can be 3-15 g/m2, preferably 5-10 g/m².

The packaging material to be manufactured according to the invention canbe formed of packaging board (paperboard/cardboard), the weight of thefibre base of which can vary between 130 and 500 g/m², being mostpreferably 170-300 g/m². A three-layer board generally used, forexample, in polymer-coated packaging boards is applicable as the fibrebase, a thicker layer of chemi-thermomechanical pulp (CTMP) of the boardbeing placed between two thinner layers of sulphate pulp. In addition,the invention covers the packaging papers, in which the weight of thefibre base is generally 20-120 g/m², preferably 40-100 g/m².

The sealed package according to the invention is formed by folding andheat sealing from some packaging material described above andmanufactured according to the invention so that the exterior surface ofthe package will contain a water vapour barrier layer containing COC andan external heat sealing layer. In this way, above all, the moistureproblem of the fibre base and the product, caused by moisturepenetrating from the outside, has thus been solved in the package.

Further, the package of the invention advantageously comprises a secondCOC water vapour barrier layer and a possible polymeric oxygen barrierlayer, which are left to the interior surface of the package inside thefibre base when the material is folded.

The package of the invention can especially be a carton or box packageformed of polymer-coated board, or a bag package formed ofpolymer-coated paper. Especially dry and liquid foods can be mentionedas products to be packed.

The invention is next explained in more detail with the help ofexamples, referring to the enclosed drawings, in which

FIGS. 1-13 present the layer structures of the packaging materials ofthe invention as different embodiment alternatives,

FIG. 14 presents a carton package of the invention, manufactured ofpackaging board by folding and heat sealing, and

FIG. 15 is a diagram of the results of the curling measurementsperformed.

The polymer-coated packaging board shown in FIG. 1 comprises in the saidorder the LDPE heat sealing layer 1, the COC water vapour barrier layer2, the fibre base 3, which is, for example, a three-layer boardconsisting of two sulphate pulp layers and a layer ofchemi-thermomechanical pulp (GTMP) between them, the COC water vapourbarrier layer 7, and the LDPE heat sealing layer 8. The LDPE and COClayers (1, 2; 7, 8) have been applied to both sides of the fibre base(3) in one step by coextrusion. The weight of the fibre base is, forexample, 250 g/m², the weight of both the COC layers 2,7 is, forexample, 15 g/m², and the weight of both the LDPE layers 1, 8 is, forexample, 15 g/m². Thus, the board has a completely symmetrical structureso that either one of the LDPE layers 1, 8 can be the exterior surfaceof the package folded from board, and either one can be the interiorsurface. Due to the water vapour barrier on both sides, the board isespecially suitable for the packaging of dry foods in countries, inwhich the climate is warm and damp.

The packaging board in FIG. 2 comprises in the said order the LDPE heatsealing layer 1, the COC water vapour barrier layer 2, the fibre base 3,the EVOH oxygen barrier layer 5, the binding agent layer 6 of, forexample, graft polyethylene, and the LDPE heat sealing layer 8. Thesuperimposed coating layers (1, 2; 5, 6, 8) on both sides of the fibrebase (3) are produced by coextrusion. The fibre base 3 can consist ofthe above-mentioned three-layer board, the weight of which is 250 g/m².The weight of the first LDPE layer and the COC layer 2 can be 15 g/m².The weight of the EVOH layer 5 can be, for example, 5 g/m², and theweight of the binding agent layer 6 can be 5 g/m² as well. The weight ofthe second LDPE layer 8 is, for example, 40 g/m². The board is meant tobe folded to a package so that the first, thinner LDPE layer 1 will bethe exterior surface of the package and the second, thicker LDPE layer 8will be its interior surface so that the EVOH oxygen barrier layer 5 isleft inside the fibre base 3 in the package. The board is usable forpackages for dry or liquid foods, in which the COC layer 2 protects theinner surfaces of the material and, when required, the product fromexternal moisture, and the EVOH layer 5 and the thicker LDPE layer 8innermost in the package protect the product from oxidation and thefibre base 3 of the material from moistening caused by the product.

The packaging board according to FIG. 3 differs from the one shown inFIG. 2 only in that, instead of EVOH, the PA layer 4 is used as theoxygen barrier, the thickness of which is, for example, 7 g/m².

In FIG. 4, there is further shown an embodiment of the board of theinvention, in which the oxygen barrier consists of superimposed PA andEVOH layers 4, 5. The weight of both these layers 4, 5 can be, forexample, 5 g/m².

In FIG. 5, there is shown a packaging board, which comprises in the saidorder the LDPE heat sealing layer 1, the COC water vapour barrier layer2, the fibre base 3, the EVOH oxygen barrier layer 5, the binding agentlayer 6 of, for example, graft polyethylene, the COC water vapourbarrier layer 7, and the LDPE heat sealing layer 8. The superimposedcoating layers (1, 2; 5-8) on both sides of the fibre base (3) areproduced by coextrusion. The fibre base 3 can be made of theabove-mentioned three-layer board, and the weight of each of the LDPEand COC layers 1, 2, 7, 8 can be 15 g/m², and the weight of the EVOH andbinding agent layers 5 g/m². The board is meant to be folded to apackage so that the LDPE layer 1 mentioned first will be the exteriorsurface of the package and the LDPE layer 8 mentioned last will be theinterior surface, in which case the EVOH layer 5 I left inside the fibrebase 3 in the package. The board is especially suitable for thepackaging of liquid foods, in which case the COC layers 2, 7 on bothsides of the fibre base provide the necessary moisture protection forthe other layers of the board at the same time as the EVOH layer 5 formsthe oxygen barrier protecting the product.

The packaging board shown in FIG. 6 differs from the one shown in FIG. 5only in that, instead of EVOH, the PA layer 4 with the weight of, forexample, 7 g/m² is used as the oxygen barrier. In FIG. 7, there isfurther shown an embodiment, in which the oxygen barrier consists ofsuperimposed PA and EVOH layers 4, 5, the weight of both of which is,for example, 5 g/m².

In FIG. 8, there is shown a packaging material according to theinvention, which differs from the one shown in FIG. 1 only in that,instead of the three-layer board, the packaging paper 3′ with the weightof, for example, 80 g/m², is used as the fibre base.

FIG. 9 discloses an embodiment of the invention, in which polymericcoating layers consisting of the COC water vapour barrier layer 7 andthe outer LDPE heat sealing layer 8 are extruded only to one side of thefibre base 3. In other words, the other side of the fibre base 3 is leftwithout the polymer coating. The fibre base 3 can be made of theabove-mentioned three-layer board consisting of sulphate and CTMPlayers. Upon folding the packaging board 9 to a package, the polymericcoating layers 7, 8 can be as well the exterior surface as to theinterior surface of the package.

The packaging board according to FIG. 10 comprises the fibre base 3,which is extrusion-coated with the EVOH layer 5, the binding agent layer6, the COC layer 7, and the LDPE heat sealing layer 8, in the saidorder. The one side of the fibre base 3 is left without the coating. InFIG. 11, there is further shown a packaging board coated from one side,in which the fibre base 3 has as a coating the COC layer 10, the bindingagent layer 11, the EVOH layer 5, the binding agent layer 6, and theLDPE layer 8, in the said order. In the embodiments in FIGS. 10 and 11,the extruded COC water vapour barrier layers 7, 10 do not curl theboard, unlike the HDPE water vapour barrier. In both the embodiments,the superimposed coating layers are meant to remain inside the fibrebase 3 upon folding the package. In the structure in FIG. 11, the COClayer 10 then protects the EVOH oxygen barrier layer 5 from moisturepenetrating from the outside of the package.

In FIG. 12, there is shown a packaging board, in which the one side ofthe fibre base 3 is provided with an coextruded coating layercombination, consisting of the LDPE layer 9, the COC layer 10, thebinding agent layer 11, the EVOH layer 5, the binding agent layer 6, theCOC layer 7 and the LDPE layer 8 in the said order. The fibre base 3excluded, the layer structure is symmetrical, with which advantage isachieved in the simultaneous extrusion of the layers. Further, in thisstructure, the COC layers 10, 7 protect the EVOH oxygen barrier layer 5from moisture penetrating from both directions. The use of HDPE wouldmake this structure unusable, due to its strong tendency to curl.

In the embodiments according to FIGS. 10-12, the EVOH oxygen barrierlayer 5 can be replaced by a polyamide layer, or EVOH and polyamidelayers placed against each other can act as the oxygen barrier, as inthe structure shown in FIG. 7.

The embodiment according to FIG. 13 comprises on the one side of thefibre base 3 the coextruded COC and LDPE layers 7, 8 corresponding toFIG. 9, and the mere LDPE layer 1 on the opposite side. Upon folding thepackaging board according to FIG. 13, the COC layer 7 can as well be onthe exterior of the fibre base 4 as on the interior, depending on theprotection need of the product and the fibre base of any given time. Dueto the amorphosity of the COC, the material has no tendency to curl.

In FIG. 14, there is seen an example of the carton package 12 of theinvention, which is formed by folding and heat sealing from a packagingblank made of the packaging board according to FIG. 12. The board islocated in the package 12 so that the exterior surface of the packageoutside the fibre base 3 is provided with superimposed COC and LDPElayers 2, 1 so that the four-layer coating 5-8 containing the EVOH layer5 remains inside the fibre base 3 in the package. At the joints 13 ofthe package 12, the edges of the blank have been made to overlap, andthe LDPE layers 1, 8 of the opposite surfaces of the board have beenheat sealed tightly to each other.

The following examples further disclose the tests performed with the newpackaging boards of the invention. The COC used in the tests was TOPAS8007 D 50, a product marketed by TICONA GmbH.

Example 1 Heat Sealability of Board

The adhesiveness of COC to board and LDPE and the behaviour in heatsealing was tested by manufacturing a polymer-coated board correspondingto FIG. 9, in which the weight of the cup board forming the fibre base 3was 210 g/m², and the weight of both the coating layers 7, 8 on it was10 g/m². No problems occurred in the adhesion of the COC and LDPE layers7, 8 to each other and to the fibre base 3. Further, a coated board wasmanufactured for the heat sealing tests, in which only one LDPE layerwith the weight of 18 g/m² was provided on the same cup board base. Inthe tests, these two coated boards were heat sealed to one another indifferent circumstances, the LDPE layers against each other. The resultsof the tests have been shown in the following Table 1.

TABLE 1 ADHESIVENESS (%) IN TEMPERATURE Jointing time (s) 200° C. 225°C. 250° C. 275° C. 0.5 25% 25-50%,   50%,   25% soft not tight 1.0 50%50-75%,  50-75%, 25-50% soft not tight 2.0 75%  100%, 75-100%,  100%,not tight not tight not tight

According to the table, the jointing times were 0.5, 1.0 or 2.0 seconds,and the jointing temperature was 200, 225, 250 of 275° C. The pressureused in the jointing was 0.8 N/mm². It is seen from the results thatwith the jointing times of 0.5 and 1.0 seconds, the jointing wasinsufficient in all the tested jointing temperatures. With the jointingtime of 2.0 seconds, however, the complete (100%) jointing was achievedin the temperatures of 225 and 275° C. The result shows that byincreasing the jointing time, a tight, leak proof heat sealed joint canbe achieved. It is apparent that the jointing can be made faster byincreasing the jointing pressure.

Example 2 Curling of the Board

Three different series of packaging boards were manufactured for thetests, in which the cup board with the weight of 190 g/m² wasextrusion-coated (1) with one single LDPE layer, the weight of whichvaried between 10 and 60 g/m²; (2) with a COC layer and an outer LDPElayer so that the weight of the COC layer varied between 10 and 40 g/m²,and the weight of the LDPE layer was in each case 20 g/m²; and (3) witha three-layer structure consisting of a COC layer, HDPE layer and LDPElayer, in which the weight of the COC layer varied between 10 and 40g/m²; the weight of the HDPE layer was 10 or 15 g/m², and the weight ofthe LDPE layer was in each case 10 g/m². The curls were measured fromdisc-shaped test pieces from their opposite sides according to the ISO11556 standard. The results can be seen in the enclosed FIG. 15.

When comparing the curling of board coated with COC and LDPE layers toboards coated with LDPE only it can be seen that COC does not addcurling, compared with LDPE, but rather reduces it when the total amountof the coating polymers being the same. Whereas in a case in which thecoating combination also contained an HDPE layer, the board curlednoticeably more. Considering the non-curling of the material, theadvantageousness of COC as a water vapour barrier polymer replacing HDPEis apparent on the basis of the tests.

Example 3 Permeation of Water Vapour

The water vapour permeation (WVTR) was measured from a series ofpolymercoated packaging boards comprising the COC layer at a temperatureof 38° C. in the relative humidity of 90%. A cup board with the weightof 190 g/m² was in each case used as the fibre base 3, and extrudedmulti-layer coatings included, besides COC, a blend of COC and LDPE,high density (HD) and medium density (MD) HDPE and LDPE in layers ofdifferent thickness.

The researched structures, in which the numerical values are layerweights (g/m²), and the measured water vapour permeations (g/m²/d) wereaccording to the following Table 2.

For reference, the water vapour permeation values from a few boardscoated with HDPE/LDPE, which do not contain COC (base boards 190, 250and 270 g/m²), have been included in the table.

TABLE 2 WVTR (g/m²/d) Layer structure Board 190 + COC 10 + HDPE (HD)10 + LDPE 10 6.59 Board 190 + COC 40 + HDPE (HD) 10 + LDPE 10 2.79 Board190 + COC 10 + LDPE 20 8.37 Board 190 + COC 40 + LDPE 20 3.03 Board190 + LDPE 10 + COC 10 + LDPE 10 6.70 Board 190 + LDPE 10 + COC 40 +LDPE 10 3.21 Board 190 + COC blend 10 + HDPE (MD) 10 + LDPE 10 7.18Board 190 + COC blend 40 + HDPE (MD) 10 + LDPE 10 2.21 Referencematerials: Board 190 + LDPE 10 + HDPE 20 + LDPE 10 5.8 Board 250 + HDPE20 + LDPE 10 7.8 Board 270 + HDPE 40 + LDPE 10 4.6

It can be seen from the results that the water vapour barrier propertiesof COC are at least equivalent to those of HDPE, and it is usable assuch or blended with LDPE.

It is obvious for one skilled in the art that the embodimentpossibilities of the invention are not restricted to those shown asexamples above, but they can vary within the scope of the enclosedpatent claims.

1. Method for manufacturing a heat-sealable packaging material, in whichsuperimposed polymeric coating layers are extruded onto a fibre base,the said layers comprising an outer polymeric heat sealing layer and atleast one inner polymeric barrier layer the water vapour penetration ofwhich is lower than that of the heat sealing layer, wherein cycloolefincopolymer (COC) is incorporated in the inner polymeric barrier layer sothat the extrusion produces an amorphous layer withoutpost-crystallisation occurring in the polymer and wherein the innerpolymeric barrier layer is adhered directly to the fibre base without abinding agent between the inner polymeric barrier layer containing COCand the fibre base.
 2. Method according to claim 1, characterised inthat the superimposed coating layers placed against each other arebrought onto the fibre base in one step by coextrusion.
 3. Methodaccording to claim 1, characterised in that the barrier layer containingCOC is adhered directly to the heat sealing layer without a bindingagent between them.
 4. Method according to claim 1, characterised inthat only one side of the fibre base is coated with polymer.
 5. Methodaccording to claim 1, characterised in that the fibre base is on bothsides provided with a heat sealing layer and an inner barrier layercontaining COC.
 6. Method according to claim 1, characterised in thatthe barrier layer is formed in its entirety of COC.
 7. Method accordingto claim 1, characterised in that the barrier layer is formed of amixture of COC and low-density polyethylene (LDPE).
 8. Method accordingto claim 1, characterised in that the weight of said at least one innerpolymeric barrier layer containing COC is 5-50 g/m².
 9. The method ofclaim 8, wherein the weight of said at least one inner polymeric barrierlayer containing COC is 7-30 g/m².
 10. The method of claim 9, whereinthe weight of said at least one inner polymeric barrier layer containingCOC is 10-20 g/m².
 11. Method according to claim 1, characterised inthat the material of the heat sealing layer is low-density polyethylene(LDPE).
 12. Method according to claim 11, characterised in that theweight of the LDPE heat sealing layer is 5-50 g/m².
 13. The method ofclaim 12, wherein the weight of the LDPE heat sealing layer is 5-30g/m².
 14. The method of claim 13, wherein the weight of the LDPE heatsealing layer is 7-20 g/m².
 15. Method according to claim 1,characterised in that at least one oxygen barrier layer is incorporatedin the polymer coating.
 16. Method according to claim 15, characterisedin that one side of the fibre base is provided with a water vapourbarrier layer containing COC and an outer heat sealing layer, and theopposite side is provided with an oxygen barrier layer and an outer heatsealing layer.
 17. Method according to claim 16, characterised in thatone side of the fibre base is provided with a water vapour barrier layercontaining COC and an outer heat sealing layer, and the opposite side isprovided with an oxygen barrier layer, a water vapour barrier layercontaining COC, and an outermost heat sealing layer.
 18. Methodaccording to claim 15, characterised in that the oxygen barrier layer isformed of ethyl vinyl alcohol copolymer (EVOH), polyamide (PA), or amixture of these.
 19. Method according to claim 18, characterised inthat the weight of the oxygen barrier layer is 3-15 g/m².
 20. The methodof claim 19, wherein the weight of the oxygen barrier layer is 5-10g/m².
 21. Method according to claim 1, characterised in that a packagingboard is manufactured, the weight of the fibre base of which is 130-500g/m².
 22. The method of claim 21, wherein a packaging board ismanufactured, the weight of the fibre base of which is 170-300 g/m². 23.Method according to claim 1, characterised in that a packaging paper ismanufactured, the weight of the fibre base of which is 20-120 g/m². 24.The method of claim 23, wherein a packaging paper is manufactured, theweight of the fibre base of which is 40-100 g/m².
 25. A method formanufacturing a heat-sealable packaging material, in which superimposedpolymeric coating layers are extruded onto both sides of a fiber base,the superimposed layers on both sides of the fiber base comprising anouter polymeric heat-sealing layer and at least one inner polymericbarrier layer the water vapor penetration of which is lower than that ofthe outer heat-sealing layer, wherein said at least one inner polymericbarrier layer on both sides of the fiber base incorporates cycloolefincopolymer (COC) so that the extrusion produces an amorphous layerwithout post-crystallization occurring in the polymer and wherein bothof said inner polymeric barrier layers are adhered directly to the fiberbase without a binding agent between either of said inner polymericbarrier layers and the fiber base.